MTC Engine Performance & Tuning 4

Question 1

When diagnosing a marine engine with an oxygen sensor, a consistently high voltage (0.8-0.9V) output indicates:

Accepted Answer

A rich exhaust condition

Answer

High O2 sensor voltage (close to 1V) indicates low oxygen content in the exhaust, which is characteristic of a rich air/fuel mixture.

Question 2

What does a technician check when performing a throttle position sensor (TPS) calibration on a marine EFI engine?

Accepted Answer

That the TPS reads 0% at idle and 100% at WOT with correct voltage range

Answer

TPS calibration verifies the sensor outputs the correct minimum voltage at closed throttle (0%) and maximum voltage at wide-open throttle (100%).

Question 3

A marine engine misfires only at high RPM under load. Ignition components test normal. Which fuel system issue should be suspected?

Accepted Answer

Weak fuel pump unable to maintain pressure under high demand

Answer

A weak fuel pump may maintain adequate pressure at idle but cannot supply sufficient volume at high RPM under load, causing lean misfires.

Question 4

On a marine diesel engine, what is the purpose of the injection advance mechanism?

Accepted Answer

Advance injection timing as engine speed increases for optimum combustion

Answer

The injection advance mechanism advances fuel injection timing as RPM increases to compensate for the shorter time available for ignition delay and combustion.

Question 5

A marine engine cooling system pressure test shows a 5 psi drop over 10 minutes. This indicates:

Accepted Answer

An internal or external coolant leak

Answer

A pressure drop during a cooling system pressure test indicates coolant is escaping through an internal leak (head gasket, crack) or an external leak (hose, fitting).

(MTC) Marine Technician Certification Practice Test

(MTC) Marine Technician Certification Practice Test

MTC Engine Performance & Tuning 4